1. Field of the Invention
The present invention relates to modified poly(oxazolidone/urethane) compositions.
2. Description of the Prior Art
The prior art illustrates the sequential reaction of polyol, acid anhydride and polyepoxy compound to form a prepolymer which is then cured. For instance, in U.S. Pat. No. 3,576,903 to G. L. Groff the first step of the reaction to form the prepolymer involves reaction of acid anhydride and polyhydroxy compound to yield an acid-terminated polymer. This acid-terminated polymer is then reacted with an epoxy compound such that at least two epoxide equivalent weights are present for each carboxyl equivalent weight of acid-terminated polymer. Groff then teaches curing of this prepolymer by use of an active hydrogen compound known to react with epoxy resins (e.g., polybasic acids, cyclic anhydrides, cyclic dianhydrides, and aromatic or aliphatic diamines) rather than with any compound containing an isocyanate group.
The formation of polymers containing oxazolidone and urethane linkages by reaction of a polyisocyanate with a prepolymer formed by a two step reaction involving (1) reaction of a dicarboxylic acid or anhydride (e.g., phthalic anhydride) and saturated dihydric alcohol followed by (2) reaction with a diepoxide is described in U.S. Pat. No. 3,847,874 to Y. Murakami et al. The reaction conditions described in this patent yield a prepolymer which contains a hydroxy group at one end and a terminal epoxide group with adjacent secondary, non-terminal hydroxy group at the other end. A diisocyanate will react with such a prepolymer to form a recurring polymer unit containing urethane and oxazolidone linkages in the backbone and urethane side chains.